Building block



FIG. 1 is a perspective view of a building block embodying the new design;

FIG. 2 is a rear view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a front view thereof; and,

FIG. 7 is a bottom plan view thereof;

FIG. 8 is a perspective view of a building block embodying a modified form of the new design;

FIG. 9 is a rear view thereof;

FIG. 10 is a top plan view thereof;

FIG. 11 is a left side view thereof;

FIG. 12 is a right side view thereof;

FIG. 13 is a front view thereof; and,

FIG. 14 is a bottom plan view thereof. 

The ornamental design for a building block, substantially as shown in the drawing. 